1. Field of the Invention
The present invention relates to an electric generation control system for use on a hybrid vehicle having a propulsive electric motor energizable by a battery and an electric generator actuated by an internal combustion engine for energizing the propulsive electric motor.
2. Description of the Related Art
Growing concern in recent years over environmental protection has led to various efforts to develop for practical applications electric vehicles which have a propulsive electric motor energizable by a battery to transmit drive forces to drive wheels for propelling the electric vehicle. One of the important requirements for such electric vehicles to satisfy is that the range which they can travel without recharging the battery be maximized and the discharging of the battery be minimized for increased battery service life.
One solution disclosed in Japanese laid-open patent publication No. 3-169203 is a hybrid vehicle carrying an electric energy generating apparatus having an electric generator and an internal combustion engine for actuating the electric generator. Electric energy generated by the electric generator is supplied to charge a battery or to energize a propulsive electric motor.
While the disclosed hybrid vehicle is running, the battery energizes the electric generator to operate as an electric motor in a motor mode to start the engine. After the engine has been started, the electric generator is switched from the motor mode to a generator mode in which it is actuated by the engine to generate electric energy, and then the engine is warmed up. Thereafter, the electric generator is operated to generate an appropriate amount of electric energy depending on an operating condition of the hybrid vehicle, such as the vehicle speed of the hybrid vehicle, and the generated electric energy is supplied to the battery or the propulsive electric motor.
The electric generator is operated to generate the electric energy as follows: Depending on an operating condition of the hybrid vehicle, such as the vehicle speed of the hybrid vehicle, a target generated output for the electric generator is obtained from a predetermined data table or the like. Then, the engine is controlled to produce a power output (drive forces to actuate the electric generator) which corresponds to the target generated output. The engine is controlled by regulating, with an actuator or the like, the opening of a throttle valve (intake air control valve) of the engine into a throttle valve opening corresponding to the target generated output. The generated output of the electric generator is also increased or reduced into agreement with the target generated output by controlling an output current from the electric generator with an inverter circuit or the like. The above generator control process is carried out from time to time to cause the electric generator to generate an amount of electric energy depending on the operating condition of the hybrid vehicle.
When the above hybrid vehicle is decelerated, the propulsive electric motor is subjected to regenerative braking and operates as a generator to supply regenerated electric energy to the battery.
Therefore, if the hybrid vehicle is decelerated and the propulsive electric motor is subjected to regenerative braking when the electric energy generated by the electric generator is supplied to the propulsive electric motor and the battery during travel of the hybrid vehicle, then the electric energy generated by the electric generator is no longer supplied to the propulsive electric motor, but is supplied only to the battery. At this time, since an electric load on the generator drops sharply or is greatly reduced, a mechanical load on the engine which actuates the generator also drops sharply. As a result, the engine races, i.e., the rotational speed of the engine increases sharply, and the engine discharges unwanted exhaust emissions or suffers undue vibrations.